1. Field of the Invention
The present invention relates to a piston pump such as a piston pump used as a pump of a brake apparatus for a vehicle.
2. Description of the Related Art
An example of the type of piston pump to which the present invention relates is disclosed in Japanese Kohyo (PCT) Patent Publication No. 2003-500610. Such a piston pump typically has a piston which is installed in a bore of a pump housing which has a suction port and a discharge port and forms a pump chamber. The piston increases and decreases the volume of the pump chamber by reciprocating in the axial direction. A suction valve is provided on the piston and disposed in an inflow passage connecting the suction port and the pump chamber. The suction valve opens when the volume of the pump chamber is increasing and closes when the volume is decreasing. A discharge valve is provided on the discharge side of the pump chamber and disposed in an outflow passage connecting the discharge port and the pump chamber. The discharge valve opens when the volume of the pump chamber is decreasing and closes when the volume is increasing. Liquid flows from the suction port to the discharge port as the volume of the pump chamber increases and decreases due to reciprocating movement of the piston in the axial direction.
In the above-described piston pump, the suction valve has a valve bore provided in the piston (communicating with the suction port) and a valve seat (formed in the end portion of the valve bore closest to the pump chamber), a cylindrical retainer which is installed on the piston, a valve body which is installed inside the retainer and can seat or unseat with respect to the valve seat, and a spring which is installed between the valve body and the retainer and which biases the valve body towards the valve seat.